1. Field of the Invention
The present invention relates to a butterfly valve which is used in an intake control valve of an internal combustion engine or the like, and more particularly to a butterfly valve in which a bearing portion rotatably supporting a valve shaft pivoting a butterfly-shaped valve body is improved.
2. Description of Related Art
Conventionally, for example, in a multi-cylinder internal combustion engine, there has been known a butterfly-shaped intake control valve in which a first surge tank chamber and a second surge tank chamber are communicated by forming a partition wall in an inner portion of a surge tank of the internal combustion engine, forming the first surge tank chamber and the second surge tank chamber within the surge tank, arranging an intake control valve in a communication hole formed on the partition wall, fully closing the intake control valve so as to separate the first surge tank chamber from the second surge tank chamber, and fully opening the intake control valve so as to communicate the first surge tank chamber with the second surge tank chamber (for example, refer to Japanese Utility Model Publication No. 6-39052 and the like).
The intake control valve controls so as to fully open or fully close the valve in response to a high load low speed operation or a low load high speed operation of the internal combustion engine, thereby changing an equivalent pipe length of an intake passage, and is controlled in such a manner as to secure a high charging efficiency all around the speed range of the internal combustion engine by using an intake inertia effect. Further, in the intake control valve, the intake inertia effect is weakened if an air leak is generated at a time when the intake control valve is fully closed, so that it is impossible to sufficiently increase the charging effect. Accordingly, a high sealing property is required at the fully closing time.
This kind of intake control valve is attached to an opening portion provided in the partition wall of the surge tank, a large valve hole is provided in a plate-like valve holder attached to the opening portion thereof so as to secure a sufficient air flow rate, and the butterfly valve is supported to the valve hole via a valve shaft so as to freely open and close. Since the valve hole is formed large in a large opening state, there is considered a structure having an elongated valve hole as shown in FIG. 10.
In the elongated large intake control valve mentioned above, a valve holder 50 thereof has a large valve hole formed in an inner side thereof, and is formed thin so as to correspond to a thin partition wall of the surge tank. Further, a large valve body is pivoted to a valve hole provided within the valve holder 50 via an elongated valve shaft 54, and slide bearings 51 and 52 receiving the valve shaft 54 are provided in both ends of the valve holder 50.
Accordingly, even if the slide bearings 51 and 52 fixed to both ends of the valve holder 50 are arranged on the same axis on design, a displacement is easily generated at a position of the axis of the slide bearings 51 and 52 at both ends due to a deformation of the valve holder 50 at a time of manufacturing or the like. In the case that the axial position of the slide bearings 51 and 52 at both ends is largely displaced, it is impossible to fit the valve shaft 54 to both of the slide bearings 51 and 52. Thus, it is necessary to provide a certain level of gap for fitting the valve shaft 54 to both of the slide bearings 51 and 52, and there is a risk that an airtightness at the fully closing time is deteriorated due to the gap generated between the valve shaft 54 and both of the slide bearings 51 and 52, and an air leak is generated at a time of fully closing the butterfly valve. Further, if the large gap exists in the fitting between the valve shaft 54 and both of the slide bearings 51 and 52, a play is generated in a motion of the valve body of the butterfly valve, and there is a risk that a problem is generated in an opening and closing operation of the valve.
Then, it is considered to arrange a self-aligning bearing as described in Japanese Unexamined Patent Publication No. 55-161259 in the bearing of the butterfly valve 53 mounted to the valve holder 50. However, since this kind of self-aligning slide bearing is formed so that an outer peripheral surface thereof has a spherical surface of a fixed diameter, it is necessary to mount a concave spherical supporting portion for movably holding the spherical surface in an outer side of the bearing, so that there are problems that the structure is complicated, a number of parts is increased, and a manufacturing cost is increased.
In accordance with the present invention, there is provided a butterfly valve comprising:
a pair of slide bearings arranged on the same axis in both sides with respect to a valve hole;
a valve shaft rotatably supported to the slide bearings; and
a butterfly-shaped valve body fixed to the valve shaft and opening and closing the valve hole in correspondence to a rotation of the valve shaft,
wherein an inner peripheral surface which is in contact with the valve shaft in the slide bearings in both sides is formed by a convex curved surface protruding to an inner peripheral side, and an inner peripheral surface shape of the slide bearing in a cross section along an axial direction is formed in a circular arc shape.
An object of the present invention is to provide a butterfly valve which has a simple structure, can be manufactured with a low cost, makes a gap between an inner peripheral surface of the slide bearing and an outer peripheral surface of the valve shaft minimum, absorbs a displacement of an axial position in the bearings in both sides, and can minimize a fluid leak at a time of being fully closed.
In accordance with the butterfly valve of the present invention, the structure is made such that the inner peripheral surface which is in contact with the valve shaft in the slide bearings in both sides is formed by the convex curved surface protruding to the inner peripheral side, and the inner peripheral surface shape of the slide bearing in the cross section along the axial direction is formed in the circular arc shape, whereby the inner peripheral surface of the bearing becomes in contact with the outer peripheral surface of the valve shaft in an substantially line contact manner. Accordingly, even in the case that the valve holder to which both of the slide bearings are mounted is deformed at a time of manufacturing, and the displacement is generated in the axial position of the slide bearings at both ends, the bearings at both ends move so as to absorb the displacement of the axis, so that it is possible to well fit the valve shaft to both of the slide bearings. Further, since the inner peripheral surface of the bearing is in contact with the outer peripheral surface of the valve shaft in the substantially line contact manner, the gap therebetween becomes minimum, so that it is possible to minimize the fluid leak at a time of being fully closed. Further, since the inner peripheral surface of the bearing is in contact with the outer peripheral surface of the valve shaft in the approximately line contact manner, it is possible to well absorb an incline or a displacement generated between the bearings in both sides due to a vibration, a heat deformation or the like at a time of using, both of the bearings serve a self-aligning operation, and it is possible to secure an improved opening and closing operation of the valve.